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I searched through the various articles trying to find that number, but no go. Maybe they're missing a zero... or perhaps 450W is actually a lot on a system that is likely drawing continuous power off a solar panel/battery.

Considering the computer power needed to go to the moon, it's not likely that this thing needs an 3.2Ghz processor and GeForce:-)

My Epia-M is plugged in taking about less than 30W of power (including HDD and DVD-ROM)... so really the equivilent of an efficient 1Ghz processor wouldn't need anything near your desktop machine's draw.

Cassini is powered by the heat of decay of plutonium creating a variation in temperature across a junction of two different metals, which creates electric power (thermoelectrics). It's called an RTG: Radioisotope Thermoelectric Generator. They're not very efficient, but you try carrying a pebble bed reactor into space and operating it by long-distance remote control in zero g.....;)

Yeah, but you aren't just powering the computer. You are also running all the radio equipment, sensors, and supporting electronics. And also remember that a lot of the supporting electronics are fault tolerant, so you are running 3 times what you need, all on hardware designed in the early 90's.

Just so. Unless they're going with USB2.0 for all the peripherals, I'm guessing that such a setup doesn't really compare to the desktop PC. Heck, even (as mentioned VIA vs AMD vs Intel) many PC's don't compare overly well... so I'm sure that 450W could be a reasonable number for whatever they're running.

Besides, part of the power of a PC is the flexibility (it can be a calculator, gaming rig, media box, etc etc). With a specialized piece of hardware such as a satellite, I'm sure that having there are mor

RTGs decrease in power production over time (since we're dealing with half lifes here). It has three RTGs which, initially, produced 285 watts of power each. With a half life of 87 years for Pu238, they should be somewhere around 250 watts each currently, so that sounds reasonable...

450 may not sound like a lot, until
you have to generate it for yourself years on end.

Your little computer is a lot bigger if you include the size of the Power Station it is attached to through a long peice of wire.

Someone should calculate how the amount of coal or oil that would
be needed to provide power for Cassini if it weren't nuclear. Or the size of solar cells needed at that distance from the sun (and their wieight).

That's pretty easy to do. Look up the enthalpy of combustion for fuel oil and coal. Any good thermodynamic textbook will have both. The unit for enthalpy is KJ/g (Kilojoules per gram of fuel.) A watt is 1 joule per second. (Isn't metric lovely?)

I googled around and found some stats from the power industry as "energy density of fossil fuel"

Oh yeah, and double all those amounts. That is the theoretical maximum that could be derived from the fuel. In practice, the best we can achieve is 40 percent. (In an industrial setting, small vehicle's like cars are lucky to get 10%).

Oh yeah, and double all those amounts. That is the theoretical maximum that could be derived from the fuel. In practice, the best we can achieve is 40 percent.

Are you sure? That's pretty close to true on earth, where the cold side of a Carnot cycle is going to be at around 300 K. Space, however, is mostly a nice, big, cold blackbody at around 3 kelvin or so (cosmic microwave background.) That should help quite a bit.

On the other hand, other posters have noted that the mass calculation neglects the o

Let's assume that Cassini averages needing 700 watts over the course of its lifetime, and lets assume a lifetime of 18 years. That's about 80 MWh of power. Assuming a 40% efficiency diesel engine burning gasoline and oxygen (have to take the O2 with you!)...

Gasoline has an energy density of 45.8 MJ/kg. Since 2 molecule of gasoline requires about 25 molecules oxygen (O2) to react, you have a molar ratio of 1 mole gasoline to 12.5 moles oxygen. 1 mole of gasoline mass about 114 grams; 12.5 moles of o2 mass about 400 grams. So, your overall energy density is about 10.2 MJ/kg.

Yeah but it's directional signal coming from the probe. 0.5 kilowatts of narrow-beam signal goes a lot farther than 10 kilowatts broadcasted from an omnidirectional antenna. But you need dishes at both ends, and they have to be aligned correctly.

I'm sure I'm not using the correct terminology (in case HAM radio experts are reading this) but that is the gist of it.

for transmitting from millions of miles away and some HAMs are using 10 kilowatts upwards just for transmitting earth-to-earth!

Some, but it is considered very bad form to use more power than necessary. Transmitting across the ground is very different than transmitting through the space. Line of sight drastically reduces the ammount of power you need, as well as using directional antenas.

The travelling-wave amplifier gives only 20 Watts of output power, which feeds into a 4 meter dish antenna. At 8.4 GHz this gives a gain of about 50 dB. EIRP then at 2 MW. (And a free space loss to Saturnus of about 300 dB....)

"some HAMs are using 10 kilowatts upwards just for transmitting earth-to-earth!"

Actually, ignoring the 1.5KW max Ham radio ops are legally bound to, most Ham operators operate in the 100 watt range (in the HF freqs == "shortwave"), and there's a dedicated core of low-power enthusiasts who communicate around the world on 5 watts, 1 watt or even a few hundred milliwatts. (The microwatt crew even come out during favorable solar conditions).

Remember when Greenpeace and other eco-idiologists wanted to abort the Hygens-Cassini mission due to the Plutonium batteries because they might drop back on earth and contain TEH EVIL RADIOACTIVE PLUTONIUM which would kill seals and cute little children ?
Lucky the officials at NASA and ESA weren't that stupid and fought off this attack.
The tremendous success of this mission illustrates how these 21th century idiologists are could stiffle science and cause harm for the whole world.
It makes me wonder if we could get this done today or in year with the eco rising to power in Europe and perhaps US after the elections, too.

Airborne plutonium dust is nothing to sniff at. Plutonium is harmless as a solid, but in dust form it's very toxic. Of course, so are the vapors from the rocket's propellent tanks, just about every combusted plastic and rubber compound on the spacecraft, and all the vaporized metal.

Yes, the greenies were making a mountain out of a molehill. Nuclear powered satellites have been launched for years, and the reactors are specifically designed to survive the destruction of the spacecraft.

The problem is that we live in a world that is only willing to offer 30 seconds of attention about any subject at a time.

...This is your last chance. After this there is no turning back. You take the blue pill, the story ends and we go back to play-bite death-matching. You take the red pill, and I tell you the truth about... Hey! Kiki?!?! NO! Zoe, she ate BOTH pills!

Vacuum of space? It was a vacuum - until you threw your melting spacecraft garbage there! Now its only a near-vacuum with Plutonium dust! Damn you NASA!!! You've ruined the last untouched region of the universe.

Lots of people are saying that Cassini uses a nuclear reactor... this is not the case as Cassini actually uses 3 Radioisotope Thermoelectric Generators (RTG) [doe.gov]. RTGs are different from reactors in that they are much simpler devices which produce electricity directly from the decay of radioactive material, in this case PU-238. Reactors on the other hand produce power from heat generated by a controlled nuclear chain-reaction.

Ok. That's like saying a wristwatch is not a chronomiter because it isn't mounted to the bridge of a ship.

If it ticks like a clock, and keeps time like a clock, it's a clock. If it harnesses energy from the decay of nuclear elements, and it does so by converting heat to electricity, it's a Nuclear reactor.

If it ticks like a clock, and keeps time like a clock, it's a clock. If it harnesses energy from the decay of nuclear elements, and it does so by converting heat to electricity, it's a Nuclear reactor.

There are some very significant differences. A Nuclear reactor involves an induced chain reaction. This is just harnessing energy from passive decay. RTG's last a lot longer, but produce less power.

Of course, your ability to post about this success came about as a result of your non dying when a potentially fatal accident didn't happen. Had the accident occurred and killed you, we wouldn't have to listen to your disdain of the ecologists.

Hearing sounds from Saturn is nothing new. My 1997 SL1 (like most old Saturns) is VERY noisy... you can hear it coming from a mile away. Step on the gas and it sounds like the power steering pump is going to pop through the hood.

The rings of Saturn have puzzled astronomers ever since they were discovered by Galileo in 1610, during the first telescopic observations of the night sky. The puzzles have only increased since Voyagers 1 and 2 imaged the ring system extensively in 1980 and 1981. In addition to the images, several Voyager instruments observed occultations of the ring system with radial resolution as fine as 100 meters. The rings have been given letter names in the order of their discovery. The main rings are, working outwar

I can't answer for the thickness of the rings, but it was mentioned in a few of the articles that NASA is trying to stay as far away from the rings as possible. The closest approach will be from above the rings and the rest of the photographs will be taken from the top of the rings. Other than that, they consider them a collision hazard...

yea but isnt the probe supposed to fly through a gap in the rings? it'd be great to get a photo taken "at level".

It is flying through a visible gap, and it's an area that seems to be clear of debris according to all the analysis done so far. But it could just be that the debris is so sparse that it's not visible.The entry point is actually well outside the visible rings, but there is another very faint ring (G ring) even farther out.

NASA realized this during the design phase, which is why they are rota

In a nutshell, here's how Cassini will interact with the rings during the orbital insertion.

Saturn right now is tilted, so that the south/"bottom" side of its rings is facing towards the Sun and Earth. Hence, Cassini is approaching Saturn from "underneath" as we see it from Earth. The orbit insertion requires Cassini to pass through the equatorial/ring plane south-to-north as it approaches the planet. It will fire its rocket while on the north side of the rings, and then coast back to the south side on its way back out.

Now, how is Cassini doing that safely? It's doing so by going through the ring plane where there are no rings. It could be thought of as a "gap", but Cassini really isn't anywhere near the rings when it crosses them. The crossing points are far outside the main mass of the ring system.

A rough analogy is this. Suppose you lived in Alaska, and had a sailboat named Cassini. Now suppose you had to sail from Alaska to Mexico without bumping into anything. Naturally, you'd pass between Hawaii and the continental US. That's a rough analogue to what's going on at Saturn - the main mass of the rings is like the continental US landmass (and there's a few small intra-ring gaps like the Mississippi River), while there's a few small outside rings sort of like the Hawaiian islands.

Would it be possible that your sailboat bumped into a rock or debris or something that we didn't know was there? Yes. Is that possibility remote enough that it makes for the safest course to your destination? Also yes.

You know, though... when people complain about there being sound in the middle of a big space battle, it always kind of bothers me a bit. Because if you were in space with space ships and missiles blowing up all around you, you *would* hear the sound of explosions as the pressurized gasses and debris from the ship expand in a shock wave travelling at speeds probably quite similar to what we're used to for sound. Sure, it would be all sudden bursts as your spacecraft was hit by the shockwaves, with no prolonged rumbles, but there *would be sound* to a viewer in a spacecraft somewhere.

And then there's the other things that could possibly cause sound - some of these futurisitic engines are supposed to be powerful ion drives or plasma thrusters, which means that there are very powerful magnetic fields being used and streams of high-velocity charged particles, both of which could possibly have an impact on certain parts of your spacecraft when you get close and make noise. If a beam weapon starts cutting at your ship's hull, your hull is definitely going to make some noise, especially when mechanical components are damaged or gasses start to leak. Etc. There would be lots of sound in a space battle.

You would hear sounds inside the spacecraft for sure - in fact, one of the biggest complaints about life on the ISS is noise from all the equipment that is operating, it is very difficult to sleep through all the fans, pumps, and various apparatus turning on and off 24/7.

But from outside, you wouldn't hear anything, unless electrical interference from the ship's system or natural sources was being picked up by your space suit radio. What is interesting, is that astronouts can communicate without radios if

How did they get sound? There is no sound in space (since it requires a medium like the air)... My guess is that the frequency of these "sounds" is close to that of the radiation being measured... Does anyone have the complete information on this?

Simply reading the related article tells us that Cassini records the radio emission from the interaction between charged particles and Saturn's magnetic field (in order to measure its rotation rate). These radio waves are in the range of 50 to 500 kHz. The 100-300 kHz band was shifted to the audible 0-3 kHz band to produce the sounds.

People theorizing about asteroid mining in the past had talked about complicated ways of getting ice out of the rare ice-bearing asteroids. Now that we know Phoebe is icy, I wonder if it ends up being the most practical place in the solar system to get ice. Although it's in the outer solar system, which is inconvenient, that's not necessarily such a big deal with solar-powered ion drive propulsion (as demonstrated by NASA already), which theoretically allows you to send anything into any orbit without paying for energy.

I guess it depends on the application, but I don't see solar working further out than Jupiter, and really you should be much closer (say Mars or Earth). Incidentally, I've run across multiple definitions of "deep space" from 2,000,000 km [bldrdoc.gov] to an region "outside" [hyperdictionary.com] the solar system. Very far from the Sun seems a good definition as any.:-)

Solar power doesn't provide a lot of energy in deep space.
Solar-powered ion drives don't require a lot of power; they use low thrust over long periods of time. Check out this link [nasa.gov] for an example. Note that the name of the craft is "Deep Space 1." It went to the asteroid belt, but even if it went out as far as the orbit of Saturn, it would just have to operate at lower thrust.

That why Cassini needed a nuclear reactor.Cassini doesn't have a nuclear reactor, it has a radioactive source that provides ener

A reactor, by definition, reacts to something, in this case, the impact of one neutron against another and a cascading effect of atoms splitting. It does not necessarily imply a sustained reaction.

In which case, an RTG is indeed a reactor, although nowhere near as energetic as the ones run by Exelon, for example. Naturally decaying radioactive material can cause a chain reaction, although it's almost never long-lived since the material density is almost never great enough to sustain it.

People theorizing about asteroid mining in the past had talked about complicated ways of getting ice out of the rare ice-bearing asteroids. Now that we know Phoebe is icy, I wonder if it ends up being the most practical place in the solar system to get ice.

A variant of this idea was explored by Isaac Asimov way back in the novella, The Martian Way (Galaxy Science Fiction, November 1952; subsequently republished in several collections).

The characters in the novel propose capturing chunks of ice from Saturn's ring system. We don't need to grab a whole moon--there are cubic-mile-sized chunks of ice in the rings. They might be a bit more manageable to manoeuvre. There are lots to choose from, too.

The sound they refer to is a frequency-shifted and time-compressed recording of emissions from charged particles in the magnetic field around Saturn. There is no actual "sound" there, as sound requires an athmosphere(sp?) of some sort. There's athmosphere a-plenty on Saturn (most of it IS probably gas, after all), but none near or around the probe.

Today marks an interesting first (at least as far as I have been able to tell): the NASA channel has had to choose which current space activity to put on TV.

On Wednesday there will be an EVA on the ISS right around the time the Cassini stuff will be happening. Thus, NASA TV had to choose, for the first time, which thing happening in space was more exciting.

How cool is that? There's actually enough going on up there that one TV channel is not enough!

Long ago, when I thought I wanted to be an EE, I did a couple of summer internships at JPL. I worked on the Cassini flight computer. My coworkers, especially the lead ASIC designer, were blisteringly smart people. If Cassini fails, it won't be the computer design at least!

Back then, the project was called "CRAF/Cassini" where CRAF was "Comet Rendezvous/Asteroid Flyby." CRAF was supposed to be the sister ship to Cassini, but it was cut for budgetary reasons. Too bad... with all the design work done how much could it have cost to just build another ship?

See, we were building this neat computer that would be reused on the next generation of probes, instead of having custom computer hardware for each... but of course it didn't work out that way.

I was lucky enough to see Cassini (and Galileo) in the Vehicle Assembly Facility. There was an observation deck where you could watch the guys in the clean room building the spacecraft. It was very cool to look down and realize, "that is going to Saturn." Or wherever.

Cassini is the last of the old school probe designs... a gigantic and expensive. She'll give us a heck of a show.